Win32: Fullscreen launch arg and adjustments.

This is long overdue, but this should finally close #2734. I'll probably also change how the WindowX/WindowY/WindowHeight/WindowWidth variables work in the future, to more closely resemble VBA-M. It's kinda useless to come out of fullscreen with it set to (0,0) for position and (windowwidth, windowheight) as the size. VBA-M remembers the previous sizes.

Also fixes the alt button trying to open the System Menu when in fullscreen by removing it altogether. After exiting FS it reinstates it.